1. Field
The present disclosure relates to methods of manufacturing a transistor, for instance, a method of manufacturing a High Electron Mobility Transistor (HEMT).
2. Description of the Related Art
A conventional High Electron Mobility Transistor (HEMT) includes an aluminum gallium nitride (AlGaN) layer and a gallium nitride (GaN) layer as main layers. Instead of chemical doping, modulation doping is applied to the HEMT using a polarization field generated by spontaneous polarization and piezo polarization. As a result of the modulation doping, a two-dimensional electron gas (2DEG) is generated in the GaN layer adjacent to an interface of the AlGaN layer and the GaN layer. The generated 2DEG may be used as an n-channel.
A conventional HEMT is formed by removing a 2DEG between a gate and a drain and by extending a distance between the gate and the drain. The HEMT may be used as a high voltage transistor. However, when considering integrity, there is a limit to the extension of the distance between the gate and the drain. Also, due to the characteristics of a semiconductor material, an electric field may be concentrated on the gate as the 2DEG between the gate and the drain is removed. Accordingly, the gate and intensity of the electric field near the gate may be greater than a breakdown voltage.
To address this electric field concentration issue, a HEMT using a field plate has been introduced. By using the field plate, the electric field that is concentrated on the gate may be partially dispersed. However, increasing the size of the field plate does not result in a continuous increase in the effect of the field plate. Also, with respect to the distribution of the electric field, although a peak may be relatively small when the field plate is present, the peak nevertheless exists, and the distribution of the electric field is not uniform.
It is possible to reduce the electric field concentration on the gate by p-doping or implanting ions into the interface of the AlGaN layer and the GaN layer. However, although the difference between a reference concentration and the p-doping concentration or the ion implantation concentration is relatively small, the breakdown voltage may greatly vary. Also, on-current reduction may also be relatively large. That is, a process window is relatively small with respect to the p-doping operation or the ion implantation. Thus, it is difficult to control the p-doping operation or the ion implantation and to ensure the reliability of the p-doping operation or the ion implantation.